I am using c string library's strlen function.I passed a NULL
string to it and found mysterious result.I know I am not supposed to pass NULL string but I need an explanation for it.The code looks something like this

main()
{
int k;
char *s=NULL;
strlen(s);
// k = strlen(s);
}

On my gcc compiler ,It runs fine with the comment.
but if you will remove the comment in the line
k=strlen(s);